The continuing purpose of this project is to explore the biological roles and the mechanisms involved in the regulation of cyclic nucleotides in Escherichia coli. During the past year, we studied the mechanisms by which the sugar transport system known as the phosphoenolypyruvate:glucose phosphotransferase system (PTS) influences the activity of adenylate cyclase. A kinetic analysis supported the regulation model involving a phosphorylation-de-phosphorylation mechanism. An analysis was also made of the properties of adenylate cyclase in E. coli with mutations in the PTS. The peculiar behavior of strains carrying mutations in Enzyme I of the PTS provided evidence that this protein is a regulator of adenylate cyclase.